This application claims the benefit of the Korean Application No. P2001-46116 filed on Jul. 31, 2001, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a projection display system, and more particularly, to a projection display system having project lenses that enable aberration correction and movement.
2. Discussion of the Related Art
Recently, with increase of request for a large sized screen and high picture quality, projection systems that enlarge and project small images using a projection lens have been rapidly spread.
Examples of a projection system include a front projection system and a rear projection system depending on a direction of an image projected on a screen.
The rear projection system has received much attention due to an advantage that a relatively bright image can be displayed even in a place where surroundings are bright.
A good example of the rear projection system includes a projection television.
In the projection TV, a cathode ray tube (CRT) mode has been used as a light source for displaying small images.
The projection TV of a CRT mode has a limitation in obtaining a small and lightweight size due to a weight of the CRT. For this reason, it is difficult to display a large sized screen and obtain luminance required for high resolution in the projection TV.
To solve such problems, there has been suggested a projection TV based on a flat display that can obtain a large sized screen at a thin thickness.
Examples of a flat display include liquid crystal display (LCD), plasma display panel (PDP), field emission display (FED), and electro-luminescence (EL) device.
Of them, a projection TV based on LCD projects light emitted from a light source onto the LCD and displays an image of a liquid crystal panel on a screen using a projection lens system.
Since the image is enlarged and projected on the screen using the liquid crystal panel of high picture quality and a small size, a large sized screen image can easily be obtained and a small and lightweight sized projection system can be obtained.
The projection display system based on a liquid crystal panel can obtain relatively high resolution and high luminance compared to the CRT. Therefore, it is expected that a large sized screen can be displayed.
FIG. 1 illustrates a related art projection display system based on a liquid crystal panel.
Referring to FIG. 1, the related art projection display system includes an optical engine 11, a total reflection mirror 14, and a screen 15. The optical engine 11 includes a lighting system 11, a liquid crystal panel 12, and a projection lens system 13.
The lighting system generates light and irradiates the generated light onto the liquid crystal panel 12. The liquid crystal panel 12 displays an image by controlling transmittivity of incident light from the lighting system 11 in accordance with an image signal. The projection lens system 13 enlarges and projects the image from the liquid crystal panel 12 and displays the image on the screen 15. Thus, a viewer can view the image displayed on the screen 15.
In this case, the image projected by the projection lens system 13 is totally reflected by the total reflection mirror 14 to change a light path. The image moves to the screen by the changed light path and then is displayed on the screen 15.
If the projected image is directly projected from the rear of the screen 15 without any change of the light path by the total reflection mirror 14, the thickness of the system becomes great. Accordingly, it is desirable to change the light path using the total reflection mirror 14 so as to reduce the thickness of the system.
In more detail, as shown in FIGS. 2 and 3, the related art projection display system includes first and second fly eye lenses (FEL) 22 and 24 arranged between a light source 20 and a first dichroic mirror 30, a polarizing beam splitter array (PBS array) 26, and a focusing lens 28.
The related art projection display system further includes a first total reflection mirror 32, a second dichroic mirror 34, a first relay lens 36, a green liquid crystal panel 44G, a second relay lens 36, a third total reflection mirror 42, a dichroic prism 46, a projection lens 48, and a screen 50.
The first total reflection mirror 32 is arranged between the first dichroic mirror 30 and a red liquid crystal panel 44R. The second dichroic mirror 34 and the first relay lens 36 are arranged between the first dichroic mirror 30 and a second total reflection mirror 38. The second relay lens 40 and the third total reflection mirror 42 are arranged between the second total reflection mirror 38 and a blue liquid crystal panel 44B. The dichroic prism 46 is arranged on three surfaces of the liquid crystal panels 44R, 44G, and 44B.
It is a general tendency that the aforementioned projection display system has a small size and is lightweight.
To make the size of the screen great and reduce the thickness of the system in accordance with such a general tendency, it is necessary to make a projection distance between the screen 50 and the projection lens 48 short.
The projection lens system includes a first lens group having a positive refractive power, and a second lens group having a negative refractive power. A total reflection mirror for changing the light path is disposed between the first lens group and the second lens group to form an xe2x80x9cLxe2x80x9d shaped projection lens system. Thus, the thickness and the height of the system can be reduced.
However, the xe2x80x9cLxe2x80x9d shaped projection lens system should make the negative refractive power of the second lens group great to obtain a short projection distance. In this case, aberration such as distortion, coma, and astigmatism occurs.
Accordingly, the present invention is directed to a projection display system that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a projection display system that enables aberration correction and can reduce the size of the system.
Another object of the present invention is to provide a projection display system that enables movement of lenses to obtain an image of high definition.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a projection display system includes a liquid crystal panel displaying an image, a first lens group having a positive refractive power, formed by combination of two or more lenses, and correcting aberration of incident light from the liquid crystal panel, a total reflection mirror reflecting the incident light from the first lens group in a predetermined direction, and a second lens group having a negative refractive power, formed by combination of two or more lenses, and correcting aberration of the incident light from the total reflection mirror.
The distance between the liquid crystal panel and the first and second lens groups is based on a focal distance and is determined to satisfy the following conditions:
2.0 less than bf1/f1 less than 2.8;
0.6 less than f2/f1 less than 1.0; and
4.0 less than d/f2 less than 5.0,
wherein bf1 represents a focal distance between the liquid crystal panel and a lens included in the first lens group nearest to the liquid crystal panel, fl represents a focal length of the whole projection lens system including the total reflection mirror, the first lens group, and the second lens group, f1 represents a focal distance of the first lens group, f2 represents a focal distance of the second lens group, and d represents a distance between the first and second lens groups.
The first lens group corrects chromatic aberration and spherical aberration of light while the second lens group corrects astigmatism and distortion of light.
Also, the first lens group includes at least one or more plastic non-spherical lenses having a positive refractive power while the second lens group includes at least one or more plastic non-spherical lenses having a negative refractive power.
The total reflection mirror reflects incident light from the first lens group upon the second lens group at a predetermined angle. The predetermined angle is defined as an angle xcex8 between an optical axis of the incident light from the first lens group and an optical axis of light emitted to the second lens group by being reflected by the total reflection mirror, and is within the range of 30 to 90.
The total reflection mirror is made of glass or plastic material and has a reflecting surface of a plane shape or non-spherical surface shape.
Furthermore, the first lens group focuses an image on the screen by moving at a predetermined distance or by moving a spherical lens arranged near the total reflection mirror among spherical lenses of the first lens group. The second lens group focuses an image on the screen by moving at a predetermined distance.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.